Photographic processes using silver halide have hitherto been most widely used for general photographic purposes, since such processes are excellent in photographic characteristics such as sensitivity and gradation control as compared to other photographic processes, such as electrophotography and diazo photographic process. Recently, techniques capable of easily and quickly obtaining images by changing the image forming process of a light-sensitive material using silver halide from a conventional wet processing by a developer, etc., to a dry process by heating, etc., have been developed.
Heat developable light-sensitive materials are known in this art field and, heat developable light-sensitive materials and the image forming process using these materials are described, for example, in Shashin Kogaku no Kiso (The Foundation of Photographic Technology), pages 553-555 (published by Corona K. K., 1979); Eizo Jyoho (Image Information), page 40, published April, 1978; Neblette's Handbook of Photography and Reprography, 7th Ed., pages 32-33 (published by Van Nostrand Reinhold Company, 1977); U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075, British Pat. Nos. 1,131,108 and 1,167,777, and Research Disclosure, June 1978, pages 9-15 (RD-17029).
Various processes have been proposed for obtaining color images. For example, processes for forming color images by a combination of the oxidation product of a developing agent and couplers that have been proposed include a combination of a p-phenylenediamine series reducing agent and a phenolic or active methylene coupler as described in U.S. Pat. No. 3,531,286; a combination of a p-aminophenolic reducing agent and a coupler as described in U.S. Pat. No. 3,761,270; a combination of a sulfonamidophenolic reducing agent and a coupler as described in Belgian Pat. No. 802,519 and Research Disclosure, September, 1975, pages 31 and 32; and a combination of a sulfonamidophenolic reducing agent and a 4-equivalent coupler as described in U.S. Pat. No. 4,021,240.
Also, with respect to processes for forming positive color images by a light-sensitive silver dye bleaching process, useful dyes and bleaching processes using the dyes are described, for example, in Research Disclosure, April, 1976, pages 30-32 (RD-14433); ibid., December, 1976, pages 14-15 (RD-15227); U.S. Pat. No. 4,235,957, etc.
Furthermore, an image-forming process by heat development utilizing a compound previously having a dye moiety and capable of releasing a mobile dye in correspondence or countercorrespondence to the recuction reaction of silver halide to silver in a high temperature state have been disclosed in European Patent Published Application Nos. 76,492 A and 79,056 A and Japanese Patent Application (OPI) Nos. 28928/83 and 26008/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application open to public inspection").
In these heat developable light-sensitive materials as described above, the development is performed by applying heat using, in many cases, a base as the development accelerator. However, there are problems in that it takes a considerable period of time to reduce the temperature of the light-sensitive material once heated to a high temperature, whereby the development sometimes proceeds excessively to reduce the image quality, and also even by a same heating pattern, the progress of the development deviates due to even small variations in conditions such as the environmental temperature, the heating temperature, the water content of the light-sensitive material, the heating time, etc.
As similar techniques for avoiding the occurrence of such undesirable development, a process of using an acid polymer for neutralization has been proposed in a diffusion transfer process as described, for example, in Research Disclosure, Vol. 123, page 22; ibid., Vol. 180, page 18030; British Pat. No. 2,082,787 A. However, when this process is applied to a heat developable light-sensitive material, the density of the image obtained is reduced, since the base is quickly neutralized. Also, as a compound releasing an acid upon heating, an acid component which is dissolved or releases a volatile acid at a temperature higher than 60.degree. C. is described in Japanese Patent Application (OPI) Nos. 58642/74 and 57452/75, but when the compounds proposed in these patent applications are applied to heat developable light-sensitive materials, the compounds neutralize bases before initiating the development by heating, whereby the development is inhibited to reduce the density of the images obtained.